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ANS Pharmacology - Parasympathetics Flashcards

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1
Q

Sites of action of acetylcholine in peripheral nervous system

A

Preganglionic fibers to ANS ganglia

Preganglionic fibers to adrenal medulla

Parasympathetic postganglionic fibers

Sympathetic postganglionic fibers innervating sweat glands (anomaly!)

NMJ

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2
Q

Muscarine

A

Parasympthomimetic

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3
Q

Nicotine

A

Acts as stimulant —> desensitizes sympathetic/parasympathetic

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4
Q

Acetylcholine

A

Both sympathetic / parasympathetic

Nicotinic vs muscarinic action

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5
Q

Acetylcholine biosynthesis

A

Addition of acetyl CoA to choline > ChAT choline acetyltransferase (cytoplasmic enzyme)

Pre-formed ACh transported into vesicles, no intracellular metabolizing enzymes

Choline from diet/protein metabolism (from serine)

RLS = Transport of choline into nerve terminal

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6
Q

Drugs affecting ACh synthesis / release

A

Hemicholinium : blocks choline uptake

Vesamicol : blocks transport into vesicles

Cholineacetyltransferase : none to date

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7
Q

Botulinus toxin

A

Bind to cell membrane + internalized > Block fusion of vesicles with plasma membrane (cleaves synaptobrevin) > block transmission

From Clostridium botulinum

Flaccid paralysis of muscles; death by paralysis of respiratory muscles

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8
Q

Mechanism of synaptic transmitter release

A

Nerve depolarization > voltage gated Na/Ca channels > Ca depended vesicle fusion and exocytosis > diffusion into synaptic cleft > receptor binding and activation > transmitter breakdown

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9
Q

Termination of acetylcholine action

A

Enzymatic breakdown of ACh by acetylcholinesterase

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10
Q

Acetylcholinesterase

A

Terminates ACh action at nerve terminals

Attached on pre/post-synaptic membrane by collagen-like filaments

Very rapid action, 150 microsec turnover

Cleaves bond to form Acetate/choline - choline re-uptake (RLS)

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11
Q

Pseudocholinesterase

A

Synthesized in liver, found in plasma

Function unclear

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12
Q

Nicotinic sites in PNS

A

Preganglionic fibers to all ANS ganglia

Preganglionic fibers to adrenal medulla

NMJ

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13
Q

Muscarinic sites in PNS

A

Parasympathetic post-ganglionic fibers

Sympathetic postganglionic fibers innervating sweat glands

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14
Q

Nicotinic receptors

A

Nicotinic neuronal - Nn
Nicotinic muscle - Nm

Ligand-gated ion channels “ionotropic receptors”

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15
Q

Muscarinic receptors

A

GPCR

“Metabotropic receptors”

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16
Q

Activation of Nicotinic ACh receptors

A

ANS ganglion stimulation - both sympathetic and parasympathetic

Release of EPI/NE from adrenal gland

Contractions of skeletal muscle

CNS - tremor, anxiety, sleep disturbances, resp/circ center effects

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17
Q

Nicotinic receptor structure/ activation

A

Pentameric structure; a, b, y, d subunits

Two a subunits —> each bind ACh to open channel —> Na moves in, K moves out

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18
Q

Muscarinic receptor structure/activation

A

7TM GPCR receptor

  • gland secretion (sweat, salivary, mucous, lacrimal)
  • contract smooth muscle (airway, GI, gall bladder, urinary, ureters)
  • pupillary constriction
  • relax sphincters (GI, urinary, biliary)
  • show HR

SLUMD (salivation, lacrimation, urination, defecation, miosis)

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19
Q

M2 - muscarinic type II receptor

A

Heart, smooth muscle, autonomic ganglia

Inhibitory

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20
Q

M3 - muscarinic type III receptor

A

Exocrine glands, smooth muscle, blood vessels (endothelium)

Excitatory

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21
Q

Action of M2 receptors

A

Inhibitory in cardiac muscle

Inhibition of adenyl ate cyclase + activation of K+ channels (decreases potential > harder to depolarize)

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22
Q

Action of M3 receptors

A

Excitatory in smooth muscle

Opening of plasma membrane and intracellular Ca channels

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23
Q

Parasympathomimetic drugs

Study These Flashcards
A

Therapeutic uses (agonists): ophthalmology (glaucoma), urinary tract disorders, GI tract disorders

Side effects: Salivation-lacrimation-urination-defecation-miosis; abdominal pain; severe hypotension

24
Q

Examples of parasympathomimetic drugs

Study These Flashcards
A

Acetylcholine (no significant therapeutic applications, broad spectrum, poorly absorbed orally/subq, rapidly hydrolzyed by IV admin)

MEthacholine
Carbachol
Bethanecol

25
Methacholine
Synthetic analog of acetylcholine Reduced susceptibility to hydrolysis, more selective for Muscarinic Used for diagnosis of asthma CV side effects - limited clinical use
26
Carbachol
Carbamylated ACh Resistant to AChE Both muscarinic + nicotinic activity Limited clinical use due to ganglionic stimulation Used to induce miosis, treatment of glaucoma
27
Bethanecol
Methylated + carbamylated ACh Resistant to AChE Very selective for muscarinic over nicotinic Used to test pancreatic function, treat urinary retention (stimulate bladder contraction)
28
Naturally occuring Cholinergic alkaloids
Pilocarpine - S Am shrub pilocarpus; mainly muscarinic, 100x potency of ACh; pronounced action on salivary/sweat glands; opthalmologocial use; can inc BP/tachycardia Arecoline - from “betel nut”, no therapeutic uses, previously de-wormer Muscarine - from mushroom; high dose —> death; atropine = antidote
29
Atropine
Anti muscarinic agent Naturally occuring - in Belladona M>>>>>>N receptor antagonist Tachycardia, dec intestinal contraction/motility, drying airway/sinuses/bronchodilation; pupillary dilation, tremor, CNS delusion/excitment
30
Therapeutic uses of atropine
Preanesthetic - decrease respiratory secretions OTC cold medications - dec lacrimal/nasal secretions Anti-asthmatic medication Ophthalmology - mydriasis Cough suppression in vet med with hydrocodone
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Homoatropine
Anti muscarinic More rapid onset that atropine Shorter duration of action Less potent
32
Scopolamine
Antimuscarinic Pre-anesthesia to decrease resp secretions OTC motion sickness Same peripheral action as atropine, but pronounced sedative action Sedate mentally ill patients
33
Propantheline
Synthetic antimuscarinic No BBB penetration - no CNS unless high dose Mitigate GI spasm/secretions (spasmodic colic in horses) Reduce rectal tearing risk in rectal exam Reduce spasm/promote relaxation of esophagus during choke in horses
34
Tropicamide
Short duration of action Used in ophthalmology > mydriasis Short recovery time (preferred over atropine)
35
Iris/lens innervation
Parasympathetic —> miosis (contract); muscarinic agonist same effect Sympathetic —> mydriasis (dilate); muscarinic antagonists same effect
36
Mydriasis
Radial (dilator) muscle - contraction causes pupil dilation, innervated by sympathetic Muscarinic antagonists
37
Miosis
Circular (sphincter) muscle - constriction of pupil, innervated by parasympathetic Muscarinic agonist
38
Ciliary muscle
Contraction —> lens bulges - near vision accommodated Relaxation - lens flattens - far vision accommodated Innervated by parasympathetic system (ACh mediated)
39
Cyclopelgia
Paralysis of ciliary muscle - lack ability to accommodate Can happen with too much or too little ACh
40
Paralysis of Accomodation
Muscarinic antagonist —> simulates too little ACh present Absence of contraction —> lungs flatted; far-sightedness
41
Spasm of accomodation
Muscarinic agonists of AChE inhibitors —> simulate too much ACh Ciliary muscle constant maximal contraction > lens budged; near sightedness
42
Treatment of narrow angle (acute congestive) glaucoma
Miosis with pilocarpine and physostigmine > inc drainage Reduce pressure until surgery Muscarinic antagonists can precipitate an attack
43
Treatment of wide angle (open angle, chronic, simple) glaucoma
Surgery! Mechanism of drug action unclear Use pilocarpine/physostigmine
44
B-blockers in the eye
Decrease production of aqueous humor
45
Synthetic nicotinic agents
Directly or indirectly modify Nicotinic Cholinergic receptor activity Ganglionic stimulants Ganglionic blockers AChE inhibitors
46
Ganglionic stimulants
Nicotine - complex often unpredictable physiological responses, stimulation + desensitization; CNS effects; stimulates adrenal medulla to release NE/EPI, Nicotinic receptor in skeletal muscle (no significant therapeutic uses)
47
Ganglionic blockers
Hexamethonium - blocks ganglionic nicotinic receptors (Nn) not Nm; limited use - both sympathetic/parasympathetic Trimethaphan - has been used in vet med to lower BP during surgery
48
AChE inhibitors
Inhibit breakdown of ACh —> parasympathomimetic Side effects: muscarinic actions at autonomic effector organs, nicotinic action at ANS ganglia, nicotinic stim at NMJ (followed by desensitization > flaccid paralysis), CNS effects
49
Classes of AChE inhibitors
Reversible inhibitors - reversible Carbamylating inhibitors - prolonged Phosphorylation inhibitors - irreversible
50
Reversible AChE inhibitor
Edrophonium Competitive inhibitor, no covalent attachment Rapidly reversible, short acting Used to diagnosis Myasthenia gravis (weakness of contraction due to decrease in receptor density at NMJ)
51
Carbamylated inhibitors of AChE
Breakdown produces carbamate vs acetate —> much slower to release
52
Physostigmine
Plant derived alkaloid AChE inhibitor Absorbed well from GI, crosses BBB Originally used in myasthenia gravis to inc ACh at NMJ Used in glaucoma Used in atropine poisoning
53
Other carbamylating AChE inhibitors
Neostigmine (only peripheral effects - used currently to treat myasthenia gravis, no BBB cross) Pyridostigmine (shorter half life) Demecarium
54
Phosphorylation inhibitors of AChE
Organophosphate Diisopropyl fluorophosphoric acid used in insecticide products synthesis of new AChE required to recover Nerve gases, Sarin, VX gas
55
Toxicology of O-P poisoning
1. Overstimulation of muscarinic / nicotinic ACh receptors (SLUMD) 2. Overstimulation of ACh receptors at NMJ in skeletal muscle 3. Paralysis of diaphragm / thoracic muscles > resp failure 4. CNS effect
56
O-P poisoning antidote
Pralidoxime (2-PAM) Phosphate acceptor Only effective before “aging” process (1-3 h)
57
Therapeutic uses of anticholinesterases
Glaucoma During Anethesia Myasthenia gravis Atropine poisoning

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